Diamond Blackfan Anemia (DBA) is a heterogeneous disease in which patients present with pure red cell aplasia, congenital abnormalities, and an increased risk of cancer. Mutations in ribosomal protein subunits (RPS) 19 and 11 have been described. We propose to characterize the molecular pathways resulting from deficiencies of RPS19 and RPL11 in the zebrafish and in mouse and human hematopoietic model systems to understand the pathogenesis of DBA. Based on our preliminary data, we will study how decreased levels of RPS19 and RPL11 alter the p53 network of proteins and the regulation of p53 through Mdm2 and other regulators. We hypothesize that p53 is differentially regulated during development. Our results and published work by others suggest that p53 is primarily regulated transcriptionally during early development, but post-translationally in more mature or adult cells. In Specific Aim 1, we will develop different zebrafish models with RPS19 or RPL11 insufficiency to characterize the role of p53 related proteins in DBA and malignant transformation. In Specific Aim 2, we will study p53 signaling pathways in human and mouse primary hematopoietic cells with RPS19 and RPL11 deficiency in vitro and in vivo. The role of inhibin as a downstream target of RPS19 insufficiency will also be investigated. In Specific Aim 3, we will evaluate known compounds regulating p53 activity in RPS19 and RPL11 knockdown hematopoietic cells as possible therapeutic approaches to treat DBA. We also propose to use zebrafish embryos to identify FDA approved drugs that rescue the RPL11 phenotype. In this manner, the signaling pathways will be linked to developmental anomalies in zebrafish and defects in hematopoiesis. Our studies will provide novel insights into the molecular pathogenesis of DBA and lead to new avenues for treatment of DBA patients.